Climate change, society, and pandemic disease in Roman Italy between 200 BCE and 600 CE

Records of past societies confronted with natural climate change can illuminate social responses to environmental stress and environment-disease connections, especially when locally constrained high–temporal resolution paleoclimate reconstructions are available. We present a temperature and precipitation reconstruction for ~200 BCE to ~600 CE, from a southern Italian marine sedimentary archive—the first high-resolution (~3 years) climate record from the heartland of the Roman Empire, stretching from the so-called Roman Climate Optimum to the Late Antique Little Ice Age. We document phases of instability and cooling from ~100 CE onward but more notably after ~130 CE. Pronounced cold phases between ~160 to 180 CE, ~245 to 275 CE, and after ~530 CE associate with pandemic disease, suggesting that climate stress interacted with social and biological variables. The importance of environment-disease dynamics in past civilizations underscores the need to incorporate health in risk assessments of climate change.

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Supplementary text Figs. S1 to S3
Tables S1 to S5 Legends for data S1 to S3 Other Supplementary Material for this manuscript includes the following:

Verification of the dinoflagellate cyst proxy
The dinoflagellate cyst proxy was verified by comparing the cyst association composition of temperature-sensitive species of the multicore GeoB 10709-5 that was collected near the study site (29) to mean Italian late summer/autumn air temperatures (32).Prior to correlation, an age model of this core has been established that takes into account the rate of sediment compaction.
The age assessment of core GeoB 10709-5 is based on 210 Pb / 137 C -dating by gamma spectroscopy at the Institute of Environmental Physics, University of Bremen (table S5).Based on the methodology described in (29), wet samples were sealed into plastic cylindrical dishes with a diameter of 7 cm using Rn tight foil.Before measurement they were left sealed for a minimum of 3 weeks so that the radioactive equilibrium between 226 Ra and 222 Rn (and its daughters) had been established.A coaxial HPGe detector Canberra Industries (50% rel.efficiency) housed in a 10 cm Pb shielding with Cu and plastic lining operated under Genie 2000 software was used for gamma spectroscopy.Measurement live-times were 2 days or more.The full energy peak efficiencies have been calculated using LabSOCS © (Laboratory Sourceless Calibration System), Genie 2000 software calibration tool, based on defined sample to detector geometry and density.For determination of excess-210 Pb activity ( 210 Pb xs ) 210 Pb -supported activity was subtracted from the 210 Pb -total signal, measured via 46.5 keV line.Supported 210 Pb was determined via the 351.9 keV line of 214 Pb.Additionally, the artificial isotope 137 C was analyzed. 137C values above the limit of detection were found in the uppermost 6 slices (down to depth of 12 cm). 210Pb xs decreases monotonously in the profile with maximum value of 106 Bq/kg in the depth of 0.5cm.
To determine the rate of compaction in the core, dry bulk densities (DBD, g/cm 3 ) have been determined every 0.25 cm.DBD has been determined by drying 1 cm 3 material overnight at 60°C directly after slicing the core.Successively the dry weight was determined using a high precision weight.Unfortunately, at several core depths, material was lost during the slicing process of the upper 9 cm of the core due to the large water content.As such reliable DBD values could only be determined for the depth intervals between 3 -4 cm and between 9 -40 cm (Data S3).The relationship between core depth and DBD has been calculated with the program Past V4.02 (97).Based on this relationship modeled DBD values have been calculated according to the equation: y = 0.21923x 0.28918 where y= modeled DBD, x = core depth (mm) The compaction of the core has been calculated with the program Past V4.02 using an exponential model..658x) where y = compaction corrected depth (mm) and x = modeled DBD (g/cm 3 ) Sedimentation rates have been determined based on the compaction adapted core depths using the 210 Pb data excluding the uppermost point (assuming a bioturbation depth of 5 cm).For this an exponential model has determined with the program Past V4.02 using a half-life time of 210 Pb of 22.2 years with the following equation: Dinoflagellate cyst processing For dinoflagellate cyst analyses, sediment samples were dried at 60°C, weighed and treated with 10% HCl and 40% HF in subsequent steps to dissolve calcium carbonate and silicate.Decantation was performed by sieving over a 20 µm high precision sieve (Storck-Veco) to prevent loss of material.The residues were transferred to an Eppendorff tube, centrifuged for 8 min at 3000 rpm after the material was concentrated to a volume of 1 ml.This material was homogenized, after which subsamples of a known volume (50-100 ml) were placed on a microscope slide, embedded in glycerin jelly and sealed with paraffin wax.Whole slides were counted for dinoflagellate cysts using a light microscope at 400x magnification.When the slides contained less than 100 specimens, additional slides were counted.Count data of core DP30PC and GeoB 10709-5 are given in Data S1 and S3 respectively.y = 928.11 (-0.020388x) -8.4199where y = 210 Pb value and x = compaction adapted core depth (mm).
This results in a sedimentation rate of 1.3835 compaction corrected mm/year (Data S3). 137Cs values above the limit of detection were found in the uppermost 12 cm.The onset of the nuclear fallout isotope 137 Cs in the core then would be expected at the depth of 6.5 cm (around year 1955), according to this model.However, penetration of the isotope into deeper layers due to continuous mixing at the top of the core can cause appearance of 137 Cs down to greater depth (approx.13 cm).The age model derived from 210 Pb is therefore not in contradiction with 137 Cs data.Table S1.Table S4.
Gravity core DP30PC 14 C dating points based on mixed planktonic foraminifera species (74).

Table S2 .
Table of epidemic outbreaks in Roman Italy (67, 99-104) Gravity core DP30PC counts of volcanic glass shards in core section 8

Table S5 .
Multicore GeoB 10709-5 210 Pb/ 137 Cs dating.Measured values of activity concentrations.Uncertainties are expressed as 1 standard deviation including counting statistics and detector calibration uncertainty.Values below decision threshold are expressed for 5% type I error probability Data S1.(separate file) Elemental composition of all analysed shards of core DP30PC in core section 8 (79 -179 cm core depth)